CN112642483A

CN112642483A - N-GQDs-PS @ CdS core-shell nano-catalyst as well as preparation method and application thereof

Info

Publication number: CN112642483A
Application number: CN202011571918.3A
Authority: CN
Inventors: 左宁; 张梦竹; 马莹莹; 孙梦; 王磊
Original assignee: Shanghai Institute of Technology
Current assignee: Shanghai Institute of Technology
Priority date: 2020-12-27
Filing date: 2020-12-27
Publication date: 2021-04-13

Abstract

The invention relates to a N-GQDs-PS @ CdS core-shell nano catalyst as well as a preparation method and application thereof, wherein the preparation method comprises the following steps: preparing N-GQDs and PS @ CdS into a mixed solution, and sequentially carrying out standing and heating reactions to obtain the N-GQDs-PS @ CdS core-shell nano-catalyst; the N-GQDs-PS @ CdS can be used as a photocatalyst and used for the photodegradation reaction of methylene blue and methyl orange. Compared with the prior art, the N-GQDs-PS @ CdS core-shell nano-catalyst prepared by the invention overcomes the problems of poor stability, easy recombination of photo-generated electrons and cavities and self-optical defects in single catalysts such as N-GQDs, CdS and the like, obviously improves the photocatalytic efficiency, can achieve 100% degradation effect on methylene blue and methyl orange within 90min under the irradiation of ultraviolet light, and further expands the application of the N-GQDs-PS @ CdS core-shell nano-catalyst in the aspect of photocatalysis.

Description

N-GQDs-PS @ CdS core-shell nano-catalyst as well as preparation method and application thereof

Technical Field

The invention belongs to the technical field of photocatalysts, and relates to an N-GQDs-PS @ CdS core-shell nano catalyst, and a preparation method and application thereof.

Background

The catalyst is discovered by Beglerius, a Swedish chemist, has a history of more than 100 years, has a plurality of types, and has important and wide application in chemical production. Wherein the photocatalyst is used as an important branch in the catalyst, and Fujishima adopts TiO under ultraviolet irradiation in 1972₂Found when water is degraded. Since then, the research heat of semiconductor photocatalysts is brought forward, and the photocatalytic degradation of pollutants becomes one of the widely-focused research directions. The photocatalyst is usually TiO₂The general name of a substance which is subjected to photocatalytic degradation based on semiconductor materials such as silver-based materials, tungsten-based materials, ZnO, CdS and the like mainly utilizes the energy of solar light and ultraviolet light emission to excite valence band electrons in a semiconductor to jump to a high-energy conduction band, so that electrons and holes are left in the valence band, and a part of photogenerated electrons (e) are generated^-) And a cavity (h)⁺) Diffuse to the surface of the photocatalyst and finally undergo redox reaction with electrons or electron acceptors adsorbed on the surface of the photocatalyst, thereby forming a series of chemical reactions initiated by the active groups of the photocatalyst. The photocatalyst has the advantages of proper energy band potential, high chemical stability, no toxicity, no harm, high photoelectric conversion efficiency, low cost, high activity and the like, is an irreplaceable preferred material in chemical production, and is widely applied to the fields of organic synthesis, catalytic chemistry, environmental management, electrochemistry, biochemistry and the like. However, photo-generated electrons and holes generated by the conventional photocatalyst are easily recombined, so that active sites on the surface of the catalyst are lost, the photocatalytic efficiency is reduced, and further development of the photocatalyst is hindered. Therefore, the high-efficiency photocatalysis is prepared by modifying the traditional photocatalystThe preparation is imperative.

Disclosure of Invention

The invention aims to provide a N-GQDs-PS @ CdS core-shell nano-catalyst, a preparation method and application thereof, and aims to solve the problem that the existing photocatalyst is low in photocatalytic degradation efficiency on organic pollutants such as methylene blue and methyl orange.

The purpose of the invention can be realized by the following technical scheme:

a preparation method of N-GQDs-PS @ CdS core-shell nano-catalyst comprises the following steps: and preparing the N-GQDs and the PS @ CdS into a mixed solution, and sequentially carrying out standing and heating reactions to obtain the N-GQDs-PS @ CdS core-shell nano-catalyst.

Further, the mass ratio of the N-GQDs to the PS @ CdS is 1 (3-5); experiments show that the mass ratio of N-GQDs to PS @ CdS influences the dispersion effect of the N-GQDs on the surface of the PS @ CdS, and too much N-GQDs easily cause agglomeration, influence the number of effective active sites and further influence the catalytic effect; if the N-GQDs are too small, the N-GQDs cannot be fully dispersed on the surface of PS @ CdS, so that the quantity of photo-generated electrons and holes is insufficient, and the recombination probability between the photo-generated electrons and the holes is increased, thereby influencing the catalytic effect;

the standing temperature is room temperature, and the standing time is 2-6 h; experiments show that the N-GQDs can not be completely loaded on the PS @ CdS surface due to insufficient standing time, and the N-GQDs can be partially agglomerated on the PS @ CdS surface due to too long standing time, so that the catalytic effect is influenced; too high or too low a resting temperature can result in too slow growth of N-GQDs on the PS @ CdS surface.

Furthermore, in the heating reaction, inert gas is used as protective gas, the reaction temperature is 80-120 ℃, and the reaction time is 1-2 h. Wherein, the growth of N-GQDs on the surface of PS @ CdS can be inhibited when the hydrothermal reaction temperature is too high, and the growth of N-GQDs on the surface of PS @ CdS can be slowed when the hydrothermal reaction temperature is too low. The hydrothermal reaction time is too long or too short, which respectively causes partial agglomeration phenomenon or insufficient load of N-GQDs during growth on the surface of PS @ CdS, and influences the catalytic effect.

Further, the preparation method of the N-GQDs comprises the following steps: preparing a mixed aqueous solution from citric acid and urea according to a molar ratio of 1 (2-4), carrying out hydrothermal reaction at the temperature of 150-.

Further, the preparation method of PS @ CdS comprises the following steps:

1) mixing the polystyrene microsphere solution with ethanol according to the volume ratio of 1 (3-8), and carrying out ultrasonic treatment for 20-40min to obtain a polystyrene ethanol solution;

2) mixing cadmium chloride, hemipentahydrate, polyvinylpyrrolidone, thioacetamide and water to obtain an aqueous solution;

3) and uniformly mixing the polystyrene ethanol solution and the aqueous solution according to the volume ratio of (1-5) to (20), and reacting at the temperature of 70-90 ℃ for 2-3h to obtain the PS @ CdS.

Further, in step 1), the preparation method of the polystyrene microsphere solution comprises:

mixing water, sodium bicarbonate, sodium p-styrene sulfonate and styrene at 60-80 ℃, adjusting the pH value to 8-9, adding an initiator potassium persulfate under the protection of inert gas, and stirring for reaction for 10-14 hours to obtain the polystyrene microsphere solution.

Furthermore, the feeding ratio of the water, the sodium bicarbonate, the sodium p-styrene sulfonate, the styrene and the initiator is (120-180) mL, (0.02-0.08) g, (0.05-0.10) g, (20-25) mL, (0.1-0.5) g.

The N-GQDs-PS @ CdS core-shell nano-catalyst is prepared by the method.

The N-GQDs-PS @ CdS serves as a photocatalyst and can be used for photodegradation reaction of methylene blue and methyl orange.

The single photocatalyst is easy to recombine holes due to photo-generated electrons generated in the illumination process, so that the quantity of the photo-generated electrons and the holes is reduced, and the catalytic efficiency is reduced. Therefore, how to improve the effective active sites by modifying the photocatalyst or combining a plurality of photocatalysts with each other, reduce the recombination rate of photogenerated electrons and holes generated in the illumination process, and improve the photocatalytic efficiency has become a hotspot of research at present.

The modified graphene quantum dot serving as a photocatalyst integrates quantum confinement, size effect and edge effect, has the advantages of good water solubility, low biotoxicity, excellent chemical inertness, stable fluorescence, easy surface modification performance, excellent luminescence performance, adjustable band gap and the like, and has wide application prospect in the fields related to chemical sensing, biological imaging, medical treatment and energy.

The band gap of the cadmium sulfide semiconductor photocatalyst is about 2.42eV at room temperature, the response range of the cadmium sulfide semiconductor photocatalyst to visible light is wide, and light with the wavelength less than 516nm can be absorbed. Based on the strong photoresponse, the appropriate position of the redox reaction band edge and the excellent charge transport performance, the CdS is a high-efficiency, typical and low-cost photocatalyst as one of the typical representatives of the metal sulfide.

According to the invention, blue light fluorescence N-GQDs is prepared by controlling the consumption of a precursor, and then the N-GQDs is stably anchored on the surface of core-shell PS @ CdS by controlling the reaction time and the consumption of the N-GQDs and the PS @ CdS, so that the N-GQDs-PS @ CdS core-shell nano-catalyst is prepared; the N-GQDs are introduced into the surface of the PS @ CdS carrier, so that the light absorption range can be expanded, hole-electron separation is facilitated, the light defect of the surface of the PS @ CdS carrier is increased based on the synergistic effect of the N and the GQDs, a lower energy gap is formed, electrons are transferred and retained under ultraviolet light, and the catalytic efficiency of the CdS carrier is remarkably improved while the problem of the light defect of the CdS carrier is solved.

Compared with the prior art, the N-GQDs-PS @ CdS core-shell nano-catalyst prepared by the invention overcomes the problems of poor stability, easy recombination of photo-generated electrons and holes and self-optical defects of CdS in a single catalyst, remarkably improves the photocatalytic efficiency, can achieve 100% of degradation efficiency on methylene blue and methyl orange within 90min under the irradiation of ultraviolet light, and further expands the application of the N-GQDs-PS @ CdS core-shell nano-catalyst in the aspect of photocatalysis.

Drawings

FIG. 1 is an infrared spectrum of the N-GQDs-PS @ CdS core-shell nanocatalyst prepared in example 1;

FIG. 2 is a Raman spectrum of the N-GQDs-PS @ CdS core-shell nanocatalyst prepared in example 1;

FIG. 3 is a graph of the photodegradation catalytic efficiency of the N-GQDs-PS @ CdS core-shell nanocatalysts prepared in example 6 for methylene blue and methyl orange;

FIG. 4 is a photo-degradation catalysis efficiency curve of the N-GQDs nano-catalyst prepared in comparative example 1 and the PS @ CdS core-shell nano-catalyst prepared in comparative example 2 for methylene blue;

FIG. 5 is a photo-degradation catalytic efficiency curve of the N-GQDs nano-catalyst prepared in comparative example 1 and the PS @ CdS core-shell nano-catalyst prepared in comparative example 2 for methyl orange.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

A preparation method of N-GQDs-PS @ CdS core-shell nano-catalyst comprises the following steps:

1) preparation of N-GQDs: preparing a mixed aqueous solution from citric acid and urea according to a molar ratio of 1 (2-4), carrying out hydrothermal reaction for 2-6h at the temperature of 150-;

2) preparation of polystyrene microsphere solution: mixing water, sodium bicarbonate, sodium p-styrene sulfonate and styrene at 60-80 ℃, adjusting the pH value to 8-9, stirring for 20-40min in an inert gas atmosphere, adding an initiator potassium persulfate, wherein the feeding ratio of the water to the sodium bicarbonate to the sodium p-styrene sulfonate to the styrene to the initiator is (120) mL, (0.02-0.08) g, (0.05-0.10) g, (20-25) mL, (0.1-0.5) g, and then stirring for reaction for 10-14h under the protection of inert gas to obtain a milky polystyrene microsphere solution;

3) mixing the polystyrene microsphere solution with ethanol according to the volume ratio of 1 (3-8), and carrying out ultrasonic treatment for 20-40min to obtain a polystyrene ethanol solution; mixing cadmium chloride, hemipentahydrate, polyvinylpyrrolidone, thioacetamide and water to obtain an aqueous solution; uniformly mixing the polystyrene ethanol solution and the aqueous solution in a volume ratio of (1-5) to (20), and reacting at 70-90 ℃ for 2-3h to obtain PS @ CdS;

4) mixing N-GQDs powder and PS @ CdS powder according to a mass ratio of 1 (3-5), preparing a mixed aqueous solution, standing the mixed aqueous solution at room temperature for 2-6h to enable the N-GQDs to grow on the surface of the PS @ CdS, heating and refluxing the mixed aqueous solution at 80-120 ℃ in an inert gas atmosphere for 1-2h to enable the N-GQDs to further grow on the surface of the PS @ CdS, and further enabling the N-GQDs to be anchored on the surface of the PS @ CdS more stably to obtain the N-GQDs-PS @ CdS core-shell nano catalyst.

The N-GQDs-PS @ CdS core-shell nano-catalyst is prepared by the method.

The following are more detailed embodiments, and the technical solutions and the technical effects obtained by the present invention will be further described by the following embodiments.

Example 1:

a preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst comprises the following steps:

1) dissolving 0.21g of citric acid and 0.1803g of urea in 40mL of deionized water, performing ultrasonic dispersion, transferring to a 50mL hydrothermal reaction kettle, performing heat preservation reaction at 160 ℃ for 4 hours, and then sequentially cooling, performing rotary evaporation and drying to obtain blue fluorescent N-GQDs;

2) putting a 250mL three-neck flask into a water bath kettle at 70 ℃, respectively adding 150mL deionized water, 0.04g sodium bicarbonate, 0.082g sodium p-styrene sulfonate and 22mL styrene, uniformly mixing, controlling the pH value of the solution to be 8-9, stirring for 30min under the nitrogen atmosphere, adding 0.3g initiator potassium persulfate, and stirring for 12h to obtain a milky PS microsphere solution;

3) adding 2mL of PS microsphere solution into 10mL of ethanol and carrying out ultrasonic treatment for 30min to obtain a PS ethanol solution; mixing 0.111g of cadmium chloride, a semi (pentahydrate), 0.2g of polyvinylpyrrolidone, 0.1g of thioacetamide and 80mL of deionized water to obtain an aqueous solution, mixing the aqueous solution with a PS ethanol solution, transferring the mixture into a 100mL hydrothermal reaction kettle, and carrying out heat preservation reaction at 80 ℃ for 2 hours to obtain PS @ CdS;

4) dissolving 50mg of N-GQDs and 0.2g of PS @ CdS in 150mL of deionized water, standing for 4 hours to enable the N-GQDs to grow on the surface of the PS @ CdS, then transferring the mixed solution to a three-neck flask, and carrying out heat preservation reaction for 1.5 hours at 100 ℃ in a nitrogen atmosphere and under a reflux condition to enable the N-GQDs to further grow on the surface of the PS @ CdS, so that the N-GQDs are anchored on the surface of the PS @ CdS more stably, and the N-GQDs-PS @ CdS core-shell nano catalyst is obtained. The infrared spectrogram and Raman spectrogram of the core-shell nano-catalyst are shown in figures 1 and 2.

The degradation efficiency of the catalyst to methylene blue and methyl orange in 90min under ultraviolet irradiation is 86.14% and 85.26%, respectively, and the degradation efficiency is general.

Examples 2 to 7:

some reaction conditions in examples 2 to 7 are shown in Table 1, and the rest is the same as in example 1.

TABLE 1

Comparative example 1:

a N-GQDs nano-catalyst is prepared by the following steps:

dissolving 0.21g of citric acid and 0.1803g of urea in 40mL of deionized water, performing ultrasonic dispersion, transferring to a 50mL hydrothermal reaction kettle, performing heat preservation reaction at 160 ℃ for 4 hours, and then sequentially cooling, performing rotary evaporation and drying to obtain the blue fluorescent N-GQDs.

Comparative example 2:

a PS @ CdS core-shell nano-catalyst is prepared by the following steps:

1) putting a 250mL three-neck flask into a water bath kettle at 70 ℃, respectively adding 150mL deionized water, 0.04g sodium bicarbonate, 0.082g sodium p-styrene sulfonate and 22mL styrene, uniformly mixing, controlling the pH value of the solution to be 8-9, stirring for 30min under the nitrogen atmosphere, adding 0.3g initiator potassium persulfate, and stirring for 12h to obtain a milky PS microsphere solution;

2) adding 2mL of PS microsphere solution into 10mL of ethanol and carrying out ultrasonic treatment for 30min to obtain a PS ethanol solution; mixing 0.111g of cadmium chloride, a semi (pentahydrate), 0.2g of polyvinylpyrrolidone, 0.1g of thioacetamide and 80mL of deionized water to obtain an aqueous solution, mixing the aqueous solution with a PS ethanol solution, transferring the mixture into a 100mL hydrothermal reaction kettle, and carrying out heat preservation reaction at 80 ℃ for 2 hours to obtain PS @ CdS;

example 8:

in the embodiment, the N-GQDs-PS @ CdS core-shell nano-catalyst prepared in the examples 1-7, the N-GQDs nano-catalyst prepared in the comparative examples 1-2 and the PS @ CdS core-shell nano-catalyst are used for catalyzing and degrading organic pollutants such as methylene blue and methyl orange.

The specific catalytic process is as follows:

putting 30mg of the catalyst into a 150mL quartz tube, adding 10mg/L methylene blue or methyl orange solution into the quartz tube, magnetically stirring for 90min under a dark condition to achieve adsorption-desorption balance, then opening a condensed water circulating system and a reactor, carrying out photocatalytic degradation under the condition of a 500W mercury lamp, sampling at an interval of 10min, filtering supernatant by using a 0.22 mu m needle filter, measuring sample absorbance by using an ultraviolet spectrophotometer, and calculating removal rate.

The results of the catalytic reaction are shown in Table 2.

TABLE 2

Wherein, the catalytic efficiency curve of the N-GQDs-PS @ CdS core-shell nano-catalyst prepared in the embodiment 6 is shown in figure 3; the photo-degradation catalytic efficiency curves of the N-GQDs nano-catalyst prepared in the comparative example 1 and the PS @ CdS core-shell nano-catalyst prepared in the comparative example 2 for methylene blue and methyl orange are respectively shown in FIG. 4 and FIG. 5.

According to the experimental data in table 1 and table 2, the hydrothermal reaction time (step 3) between the aqueous solution containing cadmium chloride and the PS ethanol solution), the mixing ratio of N-GQDs to PS @ CdS, and the standing time (step 4)) after mixing all have great influence on the photocatalytic effect of the catalyst:

experiments show that the optimal hydrothermal reaction time is 2.5h, less CdS coating can be caused by too short hydrothermal reaction time, partial CdS aggregation can be caused by too long hydrothermal reaction time, contact area between photo-generated electrons and a catalyst is reduced, and the CdS photocatalytic effect is influenced;

the optimal standing time is 4h, at the moment, the growth condition of the N-GQDs on the PS @ CdS core-shell surface is the best, enough photo-generated electrons and holes jump between the N-GQDs and the PS @ CdS during illumination, the catalytic efficiency is favorably improved, the N-GQDs cannot completely grow on the PS @ CdS core-shell surface due to the fact that the standing time is too short, the N-GQDs are partially aggregated and dropped on the PS @ CdS core-shell surface due to the fact that the N-GQDs are partially composited with the holes during photocatalysis, and further the photocatalysis effect is influenced;

the optimal mass ratio of the N-GQDs to the PS @ CdS is 1:4, the N-GQDs have the best covering effect on the PS @ CdS, the recombination probability of photo-generated electrons and holes is greatly reduced, and the catalytic efficiency is highest.

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims

1. A preparation method of N-GQDs-PS @ CdS core-shell nano-catalyst is characterized by comprising the following steps: and preparing a mixed solution from the N-GQDs and the PS @ CdS, and sequentially carrying out standing and heating reactions to obtain the N-GQDs-PS @ CdS core-shell nano-catalyst.

2. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 1, wherein the mass ratio of the N-GQDs to the PS @ CdS is 1 (3-5);

the standing temperature is room temperature, and the standing time is 2-6 h.

3. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 1, wherein in the heating reaction, inert gas is used as shielding gas, the reaction temperature is 80-120 ℃, and the reaction time is 1-2 h.

4. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 1, wherein the preparation method of the N-GQDs comprises the following steps: and preparing a mixed aqueous solution from citric acid and urea, carrying out hydrothermal reaction, and carrying out post-treatment to obtain the N-GQDs.

5. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 4, wherein the molar ratio of the citric acid to the urea is 1 (2-4);

in the hydrothermal reaction, the reaction temperature is 150-200 ℃, and the reaction time is 2-6 h.

6. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 1, wherein the preparation method of the PS @ CdS comprises the following steps:

1) mixing the polystyrene microsphere solution with ethanol, and performing ultrasonic treatment for 20-40min to obtain a polystyrene ethanol solution;

7. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 6, wherein in the step 1), the volume ratio of the polystyrene microsphere solution to ethanol is 1 (3-8);

the preparation method of the polystyrene microsphere solution comprises the following steps:

mixing water, sodium bicarbonate, sodium p-styrene sulfonate and styrene at 60-80 ℃, adjusting the pH value to 8-9, adding an initiator under the protection of inert gas, and stirring for reaction for 10-14 hours to obtain the polystyrene microsphere solution.

8. The preparation method of the N-GQDs-PS @ CdS core-shell nano-catalyst according to claim 7, wherein the initiator comprises potassium persulfate;

the feeding ratio of the water, the sodium bicarbonate, the sodium p-styrene sulfonate, the styrene and the initiator is (120-180) mL, (0.02-0.08) g, (0.05-0.10) g, (20-25) mL, (0.1-0.5) g.

9. The N-GQDs-PS @ CdS core-shell nano-catalyst is characterized by being prepared by the method according to any one of claims 1 to 8.

10. The application of the N-GQDs-PS @ CdS core-shell nano-catalyst as claimed in claim 9, wherein the N-GQDs-PS @ CdS is used as a photocatalyst for photodegradation reaction of methylene blue and methyl orange.